Gas responsive switching device

ABSTRACT

A gas responsive switching device for detecting gas concentrations in air which uses a heated semiconductor having two electrodes embedded therein, a resistor connected in series with the electrodes and across a power source, a thyristor and relay coil connected in series across a source of power and a connection between the control electrode and a tap on said resistor. The device may also include a second relay having a coil connected in series with said voltage divider and adjusted so that both relays operate at two different gas concentrations.

United States Patent Riichiro Kasahara Kobe;

Yuichi Shirnakawa, Osaka, both of Japan 54,

May 21, 1970 Sept. 28, 1971 New Cosmos Electric Co., Ltd. Hlgashiyodogawa-ku, Osaka, Japan May 28, 1969, June 5, 1969, July 11, 1969 Japan 44/49788, 44/52642 and 44/66083 Inventors App]. No. Filed Patented Assignee Priority GAS RESPONSIVE SWITCHING DEVICE 6 Claims, 6 Drawing Figs.

US. Cl 340/237 R, 23/254 E, 317/148 B, 324/71 SN Int. Cl G08b 21/00 Field of Search 340/237; 338/34; 324/71 SN; 73/23, 25-27; 23/232 E, 254 E; 317/148 B References Cited UNITED STATES PATENTS 3,051,895 8/1962 Carson 324/71SN 3,479,257 11/1969 Shaver 23/232X OTHER REFERENCES T. Seiyama et al.; Analytical Chemistry; Vol. 38, No. 8; July, 1966; Pages 1069- 1073 copy in Art Unit 171 Primary Examiner-.lohn W. Caldwell Assistant Examiner-Daniel Myer Attorney-Eugene E. Geoffrey, Jr.

ABSTRACT: A gas responsive switching device for detecting gas concentrations in air which uses a heated semiconductor having two electrodes embedded therein, a resistor connected in series with the electrodes and across a power source, a thyristor and relay coil connected in series across a source of power and a connection between the control electrode and a tap on said resistor. The device may also include a second relay having a coil connected in series with said voltage divider and adjusted so that both relays operate at two different gas concentrations.

GAS RESPONSIV E SWITCHING DEVICE This invention relates to a switching device for performing a switching operation upon the detection of an inflammable gas and more specifically to a novel and improved circuit which will perform a normal relay operation in response to the electrical output of an element detecting the presence of inflammable gas. I

Pending US. application for Pat. Ser. No. 10,848, entitled GAS ALARM DEVICE, discloses a metal oxide semiconductor element having a high sensitivity to the presence of inflammable gas. The element includes I two coils formed of metal wire and disposed in spaced parallel relationship. The metal oxide semiconductor surrounds and encloses the two coils and may be formed of materials such as SnO ZnO, Nb,0,, Ta,0 V TiO,, and Fe o each of which has a resistance characteristic which varies materially in the presence of an inflammable gas. In the operation of the element, its surface temperature is maintained in the range of 50 C. to 300 C. by passing an appropriate heating current through one or both of the coils. At the same time a voltage of the order of 100 volts is applied between the coils, and when the element is in the presence of an inflammable gas, the current flowing between the coils increases materially.

One object of the invention raises in the utilization of the above mentioned inflammable gas detecting element to operate a relay or switching circuit for opening and closing appropriate contacts having a sufficient current capacity to control any desired apparatus.

One of a circuit in accordance with the invention includes the aforesaid inflammable gas detecting element, a relay, a thyristor or silicon controlled rectifier, voltage dividing means, one or more sources of a relatively low voltage and one or more sources of a relatively high voltage. Atleast one of the coils of the detecting element is connected to the low voltage source. A series circuit including the two coils of the detecting element and said voltage dividing means, and a second series circuit including the coil of said relay and said thyristor element are connected to the high voltage source. The gate electrode of the thyristor element is connected to a tap on the voltage dividing means. With this arrangement the relay is operated when the concentration of flammable gas in the air reaches a predetermined level by reason of the increase in current flowing between the coils of the detecting element. Apparatus which may be controlled may include an illuminating device, ventilating means for exhausting the inflammable gas or valving means to shut off the supply of inflammable gas.

Another object of the invention resides in the provision of a novel and improved circuit including an inflammable gas detector which includes means for adjusting the detector to respond to a selected gas concentration in the air. Inasmuch as the components of the gas detecting element and the associated circuitry have unavoidable manufacturing tolerances, the gas concentration required to operate the relay in each device will not necessarily be uniform. With this invention the device may readily be adjusted to respond to a selected ro predetermined gas concentration. In other cases, it may be desirable to select the particular gas concentration at which the device will respond since the concentrations of certain types of gases may be maintained at a lower level than other types of gases. With this improved circuit in accordance with the invention the gas concentration at which the device will respond can be readily adjusted and selected by adjusting the tap on the voltage dividing means.

Another object of the invention resides in the provision of a novel and improved combination of an inflammable gas detecting element and associated circuitry which will afford stable operation with increased sensitivity. While the detecting element is provided with two coiled electrodes, the utilization of the coiledrelectrodes merely facilitates manufacture and the detector will function by utilizing just one of the coils to heat the semiconductor body so that the other coil could be replaced with a straight wire or plate which would not afford any heating function. Heretofore, as described in the aforesaid pending United States application, heating current was supplied to only one of the coils, and the ends of the other coil were generally connected one to the other so that it functioned as a single electrode. The application of heating current to only one of the coils results in the heating of only one part of the semiconductor body and the unheated portion of the semiconductor bodyis not very active. Accordingly, a high degree of sensitivity and stability was not attained.

In accordance with this invention heating current is supplied to both coils which produces uniform heating of the semiconductor body and thereby affords a high degree of stability and sensitivity in the detection of gas.

Another object of the invention resides in the provision of a novel and improved electrical apparatus utilizing a single gas detecting element and incorporating separate relays which can be adjusted to operate in response to different gas concentrations. This is attained by the utilization of an additional relay in a series circuit consisting of the two coils of the detecting element and the voltage dividing means. The gas concentration at which the latter relay operates can be determined by adjusting the resistance value of the series circuit as a whole. The basic relay would be adjusted by properly setting the tap on the voltage divider. With this arrangement one relay could be used to operate a ventilating fan when the gas concentration reached one selected level while the other relay would operate an alarm should the gas concentration exceed a predetermined higher level. a

A still further object'of the invention resides in the provision of means which afford an indication of the operating or nonoperating positions of the relay. For this purpose a light emitting discharge tube such as a neon lamp or the like is connected in parallel with-the relay. The tube is arranged so that it will not be illuminated when the current through-the relay coil is small but will be illuminated when the current increases to a value sufficient to operate the relay. Under this condition the voltage drop across the relay increases sufficiently to operate the neon lamp.

The above and other objects of the invention will become more apparent from the following description and accompanying drawings forming part of this application.

In the drawings:

FIG. 1 is an enlarged perspective view of an inflammable gas detecting element used with this invention and in which the semiconductor body is shown in outline in order to illustrate the internal structure;

FlG. 2 is a transverse sectional view of a gas detecting element as illustrated in FlG. l;

FlG. 3 is a side elevational view in partial section of the mounting means for the detecting element shown in FIGS. 1 and 2;

FIG. 4 is a circuit diagram of one embodiment of a gas responsive device in accordance with the invention wherein heating current is supplied to both coils of the detecting element;

FIG. 5 is a circuit diagram of another embodiment of the invention utilizing two relays operable at different gas concentration levels; and

FIG. 6 is still another embodiment of the invention wherein neon tubes are interconnected with the relays to indicate the operational state of the relay.

Referring now to the drawings, the gas detecting element used in accordance with this invention is illustrated in FIGS. 1 and 2. The detecting element comprises a pair of coils l and 2 formed of a relatively nonoxidizable metal wire such as platinum, palladium or platinum-iridium alloy. The coils are disposed in parallel grooves 4 and 5 formed in opposing surfaces of a block 3, the latter being formed of a heat proof electrically insulating inorganic oxide such as A1 0 SiO or BeO. An inorganic high melting point adhesive 6 and 7 is used to secure the coils l and 2 in the grooves. The adhesive is preferably formed of a material such as Na,0 intermixed'with at least one of the following materials, namely, K 0, CaF

A1 0 Ba O and SiO,. With this arrangement the coils are fixed in predetermined parallel relationship. It is to be noted that only a portion of each of the coils is embedded in the adhesive so that the major portion of each coil is exposed. The block 3 and the coils l and 2 are then enclosed within a metal oxide semiconductor material 8 as will be observed more clearly in FIG. 2. The semiconductor material is sensitive at high temperatures to inflammable gas, and the completed unit forms a blocklike structure with the ends of the coils 1 and 2 extending from the structure and constituting lead wires 9, l0, 1 l and 12.

The metal oxide semiconductor material 8 is preferably formed of SnO ZnO, Nb O, Ta O V TiO or Pep, When these materials contact an flammable gas and are heated to temperatures of the order of 50 C. to 300 C., the gas removes oxygen ions from the semiconductor material and oxidizes the semiconductor material. This causes the cations and anions within the semiconductor body to become unbalanced with the result that the resistance of the semiconductor material varies.

The semiconductor element as illustrated in FIGS. 1 and 2 by then mounted within a housing as illustrated in FIG. 3. More specifically, the lead wires 9, 10 11 and 12 are connected to supporting rods l3, 14, 15 and 16 formed of a conducting material and which are carried by a stem 17. The stem 17 is formed of an insulating material such as plastic or the like, and the conductors 13 through 16 protrude from the bottom face of the stem to fonn connecting prongs. In the actual manufacture of the detecting element as shown in FIGS. 1 and 2, the coils 1 and 2 are first connected to the conductors 9 through 12. The grooves 4 and 5 of the insulating 3 are then coated with the adhesive agent 6 and 7 whereupon the block is inserted between the coils I and 2. The coils are then heated by passing a current through the supporting rods l3, l4, and 15, 16 to melt the adhesive and permanently fix the coils 1 and 2 to the block 3. The coils 1 and 2 and the block 3 are then enclosed within a nonsintered gas sensitive metal oxide semiconductor. The coils are then reheated to sinter the metal oxide semiconductor and thus form the completed detector. Inasmuch as the heating current required during actual use of the detector is substantially less then the heating current required for fabrication, neither the adhesive nor the metal oxide semiconductor will be adversely affected by the heat required for actual use of the detector.

The detecting element is enclosed by a cylindrical metal wire mesh 18 and the upper end of the mesh is closed by a metal cap 19. The stem 17 has an upper portion 20 of relatively small diameter to receive the cylindrical mesh and a lower portion 21 of greater diameter. The mesh 18 fits within a groove 22 formed in the lower portion 21 and is secured thereon by a suitable adhesive.

Referring now to Fig. 4, the inflammable gas detecting element as described above is generally denoted by the numeral 31 and the coils are denoted by the numeral 32 and 33. The electrical circuit includes a power transformer generally denoted by the numeral 34 having a binary winding 35 adapted to be energized by an alternating current voltage of 110 volts or 220 volts as may be desired. The transformer further includes a pair of secondary windings 36 and 37, each of which generate approximately 1.5 volts and a secondary winding 38 which generates approximately 100 volts. The windings 36 and 37 are connected to the coils 32 and 33, respectively, to heat the element 31. One end of the secondary winding 38 is interconnected with the secondary winding 37 and one side of the secondary winding 36 is connected through a voltage divider 39 to the other side of the winding 38. This arrangement produces a series circuit including the winding 38, the coils 33 and 32, and the voltage divider 39. A series circuit consisting of the relay coil 40 and the thyristor 41 .is connected across the winding 38 and the gate 43 of the thyristor 41 is connected to a movable tap 44 on the voltage divider 39. The relay is provided with contacts 45 which are normally open and which close when the coil 40 is energized. If desired, a capacitor 46 may be connected in parallel with the relay 40 to minimize the ripple component of the current used to energize the relay.

With the arrangement as shown in FIG. 4, when the concentration of inflammable gas in the air is very low, the resistance of the metal oxide semiconductor 42 of the element 31 is large. As a result, the current flowing between the coils 32 and 33 will be small and very low voltage will appear at the tap 44. Since this voltage is below the firing voltage of the thyristor, the impedance of the thyristor will be very high and the relay coil 40 will be effectively in a deenergized state. When the concentration of inflammable gas increases, the resistance of the detector 31 decreases. Should the concentration reach a predetermined threshold, sufficient current will flow between the coils 32 and 33 to produce a voltage at the voltage divider tap 44 sufficient to fire the thyristor and cause its impedance to decrease and produce substantial current flow through the relay coil 40 closing the contacts 45. The contacts 45 may then be utilized to control electrical apparatus connected thereto. The specific gas threshold at which the thyristor 41 will be fired can be selected by adjusting the position of the tap 44 and the voltage divider 39. Since alternating current is used to operate the relay, when the concentration of gas falls below the threshold, the voltage at the tap 44 will fall below the firing point of the thyristor, and accordingly, the thyristor will return to its maximum impedance state and deenergize the relay.

In the embodiment of the invention as illustrated in FIG. 5. components corresponding to components in FIG. 4 have been denoted by like numerals. In FIG. 5 the transformer 34 is provided with a single low voltage secondary winding 37 which provides heating current to the coil 33 of the detecting element 31. Thus the semiconductor portion 42 is heated only by the coil 33. The relay 51 has one end of the coil connected to the coil 32 while the other end of the relay coil is connected to the voltage divider 39 having a variable resistor 53 connected in parallel therewith. The operation of this circuit is substantially the same as the circuit shown in FIG. 4 in that the relay 40 will operate when the inflammable gas concentration reaches a predetermined threshold and produces a voltage on the tap 44 sufficient to fire the thyristor 41. With this embodiment of the invention the relay 51 connected in series with the detecting element 31 will be operated to close the contacts 52 when sufficient current flows through the detector 31 as a result of increases gas concentration. The threshold at which the relay 51 will operate can be controlled by the adjustment of resistor 53. When the resistor 53 has been properly adjusted, the tap 44 can be adjusted so that the relay 40 will be operated at a selected gas concentration.

With the circuit shown in FIG. 5, the two relays can be operated at different gas thresholds. This arrangement is particularly advantageous in that one relay can initiate operation of a ventilating fan when the gas concentration attains a first level and then should the concentration continue to increase, the second relay can operate an alarm device or a valve closing mechanism associated with the gas supply.

The embodiment of the invention illustrated in FIG. 6 is similar to that of FIG. 5 except that a neon lamp 54 and series resistor 55 are connected in parallel with the relay 40. A'filtering condenser may also be utilized in parallel with the relay as illustrated. A second neon lamp 56 and a series resistor 57 are connected effectively in parallel with the relay coil 51. It is preferable, however, to use a variable resistor 58 connected in parallel with the resistor 53 and to connect the lower end of the resistor 57 to an adjustable tap on the resistor 58.

When the neon lamp 54 is illuminated by reason of the firing of the thyristor 41, an immediate indication is provided showing that the relay 40 has been operated. The neon lamp 56 will be illuminated when the resistance of the semiconductor 42 of the detector 31 falls below a predetermined value. Such value however can be determined by adjusting the resistor 58. In this way the lamp 56 can be arranged to be illuminated coincidentally with the operation of the relay 51.

While only certain embodiments of the invention have been illustrated and described, it is apparent that alterations, modifications and changes may be made without departing from the true scope and spirit thereof as defined by the appended claims.

What is claimed is:

l. A gas responsive device comprising an inflammable gas detecting element having two electrodes at least one of which is a heating electrode and a metal oxide semiconductor enclosing and contacting both electrodes, said semiconductor having a resistance variable in response to the concentration of said gas in air, a first power source connected to said heating electrode for heating the said semiconductor, a second power source, a voltage divider including a tap thereon, a connection from one of said electrodes to one side of the second power source, means including said voltage divider connecting the other of said electrodes to the other side of said second power source, a relay having a coil and contacts operated by said coil, a thyristor having a control electrode, said relay coil and thyristor being connected in series across said second power source and a connection between said control electrode and the tap on said voltage divider.

2. A gas responsive device according to claim 1 wherein said other electrode is a heating electrode and said device includes a third power source connected to said other electrode whereby both electrodes are heated.

3. A gas responsive device according to claim 1 wherein said voltage divider is a resistor and said tap is adjustably positioned on said resistor.

4. A gas responsive device according to claim 1 including a second relay having a coil and contacts, the last said coil being connected in series with said voltage divider and is energized by current flowing through said detecting element.

5. A gas responsive device according to claim 1 including a light emissive discharge lamp connected in parallel with said relay coil.

6. A gas responsive device according to claim 4 including a light emissive discharge lamp connected in parallel with the coil of said secondary relay. 

1. A gas responsive device comprising an inflammable gas detecting element having two electrodes at least one of which is a heating electrode and a metal oxide semiconductor enclosing and contacting both electrodes, said semiconductor having a resistance variable in response to the concentration of said gas in air, a first power source connected to said heating electrode for heating the said semiconductor, a second power source, a voltage divider including a tap thereon, a connection from one of said electrodes to one side of the second power source, means including said voltage divider connecting the other of said electrodes to the other side of said second power source, a relay having a coil and contacts operated by said coil, a thyristor having a control electrode, said relay coil and thyristor being connected in series across said second power source and a connection between said control electrode and the tap on said voltage divider.
 2. A gas responsive device according to claim 1 wherein said other electrode is a heating electrode and said device includes a third power source cOnnected to said other electrode whereby both electrodes are heated.
 3. A gas responsive device according to claim 1 wherein said voltage divider is a resistor and said tap is adjustably positioned on said resistor.
 4. A gas responsive device according to claim 1 including a second relay having a coil and contacts, the last said coil being connected in series with said voltage divider and is energized by current flowing through said detecting element.
 5. A gas responsive device according to claim 1 including a light emissive discharge lamp connected in parallel with said relay coil.
 6. A gas responsive device according to claim 4 including a light emissive discharge lamp connected in parallel with the coil of said secondary relay. 